This invention relates to an assembly comprising a cylindrical container and a pressure control device for maintaining a constant predetermined pressure in the container which is arranged for dispensing a fluid contained in the container from the container at said pressure, the pressure control device comprising a first chamber and a second chamber as well as at least one closing member movable relative to the second chamber for releasing and closing a fluid connection between the first chamber and the container depending on the position of the closing member relative to the second chamber, the first chamber being filled with a gas which in use has a higher pressure than the pressure in the container, and the position of the closing member relative to the first chamber being at least dependent on the prevailing pressure in the container and the prevailing pressure in the second chamber, while in use the fluid connection is released when the pressure in the container decreases below the predetermined pressure, so that gas flows from the first chamber to the container and the pressure in the container increases again until the fluid connection is closed again by the closing member as a result of the increased pressure in the container, wherein the second chamber is located outside the first chamber, and the closing member comprises a stem which extends through a first opening of the first chamber wherein the first opening is provided with a sealing ring and the stem is provided with a circumferential recess where the sealing ring extends in the recess. Such an assembly is known, from EP-A-0 446 973.
A disadvantage of the known assembly is that the fluid in the container will not always be suspended in a reliable and accurate manner. This means that with the passage of time, diffusion of gas from the first chamber and the second chamber to the container will occur. Since the pressure in the second chamber determines the predetermined pressure in the container of the container, this means that the predetermined pressure over time is unstable. In addition, it is found that the closing member will not react properly to a decreasing and increasing pressure in the container. In that event, accordingly, no accurate pressure control in the container will occur.
Furthermore the closing member is provided with a membrane to which the stem is attached for opening and closing of the first chamber.
This in turn has an adverse effect on the movability of the stem for regulating the pressure. So that pressure control becomes inaccurate This also results in the above disadvantage. Finally if the container is almost empty the effective volume of the container wherein the fluid to be dispensed is present becomes relative large to the volume of the fluid which may cause an inaccurate dispense of the fluid.